For a number of applications, it is important to be able to detect the presence of microbes at a given location, for example to determine whether foodstuffs are safe for consumption or whether a wound has become infected. There are currently a number of methods for the detection of the presence or absence of microbial contamination. However, these methods generally require a multistep assay to be performed in a laboratory or other clinical environment and not directly at the location where microbial contamination may exist.
During the process of wound healing there is often a serious danger of microbes entering a wound site, multiplying and resulting in the wound becoming infected. There are currently only indirect clinical methods of determining this condition. This is usually at a point at which infection has taken hold and is considered to be seriously detrimental to the patient. In extreme cases septicaemia will result. On the other hand it is well understood that over-frequent changing of a patient's dressing leads to sub-optimal wound healing.
A number of systems have been proposed which are intended to give nursing staff a prior warning of exudate striking through the surface or edges of a dressing and hence provide an indication of when a dressing should be replaced. These include the SignaDress (Trademark) dressing, available from Bristol-Myers Squibb, which has a transparent cover sheet on which a circular line is printed. When exudate from the wound is absorbed by the dressing, an area of moisture is evident through the cover sheet, and its spreading towards the line indicates that the dressing should be changed. EP-A-0541251 discloses a pad including a substrate that allows the extent of wound exudate absorption to be viewed therethrough. WO-A-99112581 discloses a wound dressing including an indicator layer which contains a dye that changes colour on contact with water.
Other systems have been proposed, intended to give nursing staff an indication of when a dressing should be replaced. For example, EP-A-0430608 discloses a wound dressing including a temperature-sensing liquid crystal tape; there is no evident means of distinguishing the possible causes of increased temperature, which may or may not be indicative of the need to change the dressing.
Current wound management is performed largely on an entirely subjective basis. None of the systems proposed above provide an indication of wound condition or of the presence of microbial contamination at a wound site.
In the personal care, clinical nutrition, pharmaceutical, dairy, beverage and food industries, rapid and traditional microbiological methods exist to monitor product quality during and immediately following the production process. However, this approach has the disadvantage that these tests are performed on a small random selection of the total production batch, and are therefore helpful only in indicating gross contamination problems at the point of manufacture. No information on microbial activity is given to the end user up to the point at which the product is deemed to have reached the end of its shelf-life. Furthermore, once the packaging has been breached, for example by the action of opening and subsequent reuse of the product, opportunistic organisms can contaminate the product. The presence of these micro-organisms can jeopardise the quality and organoleptic characteristics of the product, compromise performance, and shorten shelf-life. Also traditional methods of microbiological detection tend to be selective and may miss certain species of organism.
Micro-organisms of particular concern include the opportunistic Pseudomonads which are environmental organisms found in soil and water. These bacteria have minimal nutritional needs and can metabolize and grow almost anywhere. Other hazardous organisms of concern to consumers include E. coli in beef, listeria on soft cheeses and salmonella in poultry.
Particularly vulnerable forms of foodstuffs include UHT (ultra heat treated)/ESL (extended shelf-life) dairy products, cook-chill products and raw meats.
Consumers are becoming more demanding and expecting products to contain more natural ingredients with fewer preservatives, together with the added requirements of having longer shelf-life and the ability to perform under difficult conditions. These customer trends are powerful and can increase the risk of contamination both at the point of manufacture and whilst the product is in use in the hands of the customer. The need therefore for a method of providing a continuing check on the level of bioburden in these products is clear.